Re: gEDA-user: Free Dog meetings at MIT starting this September!

[Dave McGuire <mcguire@neurotica.com>]

On Aug 22, 2004, at 2:23 PM, Karel Kulhavý wrote:
> > > neophyte to solder.
> >   I must strongly disagree with this statement.  The notion that
> > through-hole soldering is easier than soldering surface-mount devices
> > is, and always has been, a myth.  Personally, any more, I *hate*
> > soldering through-hole parts.  Sure it takes a steadier hand due to 
> > the
> > finer pin spacings and such, but give me an SOIC over a DIP any day.
> >
> >   Perhaps a part of the problem is that people want to be able to
> > solder with a cheap soldering iron they bought at Radio Shack for $12
> I am using transformer gun with that loop of thick wire at the end. 
> Should
> I upgrade?
  Ok, you really made me laugh with this one, which is a big surprise 
with the mood I'm in today. :-)

> Isn't it possible to get away with the sioldering without a soldering 
> iron
> at all? The manufacturing lines are using allegedly some kind of solder
> flowing in circles that makes a bulge on the surface of the liquid and
> the PCB is stuck into the bulge. At least someone has been describing 
> it to
> me this way.
  That'd be "wave soldering".  Wave soldering is useful for 
through-hole parts, but for SMT assembly, "reflow soldering" (see 
below) is the way to go.

> Isn't it possible to heat up amount of solder in an old pot or pan, 
> add a
> handful of rosin and then carefully dip the board into it?
  Sure.  But "reflow soldering" is much more practical.  I'm gearing up 
for that here right now.  You take "solder paste" (a mix of finely 
powdered solder and flux) and apply it to SMT pads with a syringe.  You 
stick the components ("pick and place") onto the board, they adhere to 
the solder paste.  This is done either manually or automatically.  Then 
you "bake" it in an oven with a very carefully controlled 
temerature/time profile until it melts, and surface tension 
automatically [mostly] centers the components on the pads.  Solder 
masks on the PCBs keep inter-pin shorts to a minimum.  The results are 
usually very clean, very consistent, and very, very reliable.

  Large multi-zone conveyor ovens are used for this in assembly houses, 
but they cost a fortune and require an immense amount of electricity to 
run.  Lately some companies have started making small benchtop reflow 
ovens (that's what I'm getting) which are practical for prototyping and 
low-volume production.  There are reports of hobbyists having success 
with VERY CAREFUL use of a household toaster oven (don't use the one 
you use for food...buy a separate one, as nasty chemicals [lead solder, 
flux] are involved!) but I would not try this for a "professional" 
application.  True purpose-built reflow ovens have very accurate 
control of their temperature, are designed for very even and very fast 
heating, and have blowers for fast cool-down.

> I have once seen in TV how some guy was casting tin soldiers this way 
> at home.
  Yup, a lot of people do that.  It's pretty easy to do.

> Someone has also described a homebuilt thru-plating station (however it
> isn't still probably a finished design yet).
  Now this is something I'd like to see. :-)  URL?

> Just add a homemade 150 000 rpm compressor-driven spindle PCB drill 
> with
> linear X-Y drives and 2um precision and you can save walking to PCB
> manufacturer (however the machine weighs 6 tons - I fear it would
> probably fall through the room's floor ;-) )
  Well...there are limits. ;)

       -Dave

--
Dave McGuire             "...it's a matter of how tightly
Cape Coral, FL             you pull the zip-tie."       -Nadine Miller